Radio communication systems, such as cellular or trunked radio systems, are known to comprise a plurality of communication units, a plurality of sites, a plurality of site controllers, and a switching center. The sites, which comprise radio infrastructure equipment, such as base stations and antenna towers, are located throughout the geographic coverage area of the radio communication system. Each site provides a predetermined number of communication resources (e.g., frequency carriers or time slots) that provide communications support for one or more of the communication units. Each site controller services a group of sites in a particular geographic service area, and is used to translate (i.e., transcode) communications received from its respective sites into a coded format that is compatible with transmission over the public switched telephone network (PSTN). Each site controller also controls the handoff between sites--i.e., reassignment--of ongoing communications in its respective service area. In a similar manner, the switching center services the sites in geographic service areas that may be similar to, or distinct from, the service areas supported by the site controllers. The switching center controls functionality of the complete radio communication system, via control portions contained therein, including communication handoffs between site controllers and interconnections to the PSTN.
In a typical system configuration, the site controllers and the switching center are collocated at a facility that is remotely located from any of the sites. Thus, to provide communications to their respective site controllers, the sites typically utilize radio frequency (RF), or microwave, links to transfer the communications to the site controllers. Accordingly, there is a significant cost associated with the transfer of information between the sites and the site controllers.
To determine which sites reside in each site controller's service area, an assignment algorithm, such as that described in U.S. Pat. No. 3,703,006, is employed to assign the sites to the site controllers such that the costs to transmit information between the sites and the site controllers are minimized. Although this transmission cost minimization is beneficial, the assignment process often produces service areas with overlapping boundaries (i.e., sites residing in more than one service area) and undesired geographic balance (e.g., service areas with long, narrow geometries). The undesired geographic balance typically results in the handing off of an inordinate amount of ongoing communications between the site controllers because the communication units, while communicating, frequently travel through (i.e., into and out of) the various undesirably configured service areas. The additional handoffs increase system cost and complicate system management.
In addition, assignment techniques of the prior art commonly produce an assignment of sites to site controllers in which some site controllers are heavily loaded (i.e., support a substantial number of communication resources) and other site controllers are lightly loaded. That is, the assignment results in a communication resource load imbalance among the site controllers of the system. Accordingly, the heavily loaded site controllers might become a reliability concern over time, while the lightly loaded site controllers contain unused, and correspondingly unnecessary, processing capabilities.
Therefore, a need exists for a method of establishing a logical connection between the sites and either the site controllers or the switching center in a radio communication system, such that geographic balance of service areas is attained, and such that communication resource loading at each site controller, or switching center control portion, is substantially balanced.